Electroluminescent devices for lighting applications

ABSTRACT

A method of fabricating an organic light emitting device is provided. A first electrode is provided, over which the rest of the device will be fabricated. A first organic layer is deposited over the first electrode via solution processing. The first organic layer includes:
         i. an organic host material of the first organic layer;   ii. a first organic emitting material of the first organic layer;   iii. a second organic emitting material of the first organic layer;       

     A second organic layer is deposited over and in direct contact with the first organic layer. The second organic layer includes an organic emitting material of the second organic layer. A second electrode is then deposited over the second organic layer. The device may include other layers.

This application claims priority to U.S. provisional application No.61/296,680, filed Jan. 20, 2010, the disclosure of which is hereinexpressly incorporated by reference in its entirety.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices, andmore particularly to organic light emitting devices that include asolution deposited emissive layer.

Organic light emitting devices (OLEDs) make use of thin organic filmsthat emit light when voltage is applied across the device. OLEDs arebecoming an increasingly interesting technology for use in applicationssuch as flat panel displays, illumination, and backlighting. SeveralOLED materials and configurations are described in U.S. Pat. Nos.5,844,363, 6,303,238, and 5,707,745, which are incorporated herein byreference in their entirety.

The color of an OLED device may be measured using CIE coordinates, whichare well known to the art. Unless otherwise specified, CIE coordinatesas used herein refer to 1931 CIE coordinates.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form. A “solution processed” layerrefers to a layer that was deposited using a liquid medium. Examples ofsolution deposition techniques include spin coating, dip coating, slotdye coating, roll-to-roll coating and ink-jet printing.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

An method of fabricating an organic light emitting device is provided. Afirst electrode is provided, over which the rest of the device will befabricated. A first organic layer is deposited over the first electrodevia solution processing. The first organic layer includes:

-   -   i. an organic host material of the first organic layer;    -   ii. a first organic emitting material of the first organic        layer;    -   iii. a second organic emitting material of the first organic        layer;        A second organic layer is deposited over and in direct contact        with the first organic layer. The second organic layer includes        an organic emitting material of the second organic layer. A        second electrode is then deposited over the second organic        layer. The device may include other layers.

Preferably, the first organic emitting material of the first organiclayer has a peak emissive wavelength in the visible spectrum of 590-700nm, the second organic emitting material of the first organic layer hasa peak emissive wavelength in the visible spectrum at 500-590 nm and theorganic emitting material of the second organic layer has a peakemissive wavelength in the visible spectrum of 400-500 nm.

Preferably, the first organic emitting material of the first organiclayer is present in the first organic layer in a concentration of 0.01-5wt %, and the second organic emitting material of the first organiclayer is present in the first organic layer in a concentration that is1.1 to 500 times the concentration of the concentration of the firstorganic emitting material. In addition, the second organic emittingmaterial of the first organic layer is present in an amount not morethan 40 wt %. Percentages are given as weight percentages of the organiclayer after fabrication, and may generally be determined by using therelative weight percentages in solution of the various materials to bedeposited, because the solvent evaporates.

More preferably, the first organic emitting material of the firstorganic layer is present in the in the first organic layer in aconcentration of 0.2-4 wt %, and the second organic emitting material ofthe first organic layer is present in the first organic layer in aconcentration that is 2 to 200 times the concentration of theconcentration of the first organic emitting material. In addition, thesecond organic emitting material of the first organic layer is presentin an amount not more than 40 wt %.

Preferably, the first organic emitting material of the first organiclayer, the second organic emitting material of the first organic layer,and the organic emitting material of the second organic layer are allsmall molecule materials.

Preferably, the second organic layer comprises an organic host and theorganic emitting material of the second organic layer. Preferably, thesecond organic layer is deposited by vapor deposition, where the organichost of the second organic layer and the organic emitting material ofthe second organic layer are co-deposited. Vapor deposition includesvapor thermal evaporation (VTE), organic vapor phase deposition (OVPD),and organic vapor jet printing (OVJP).

Preferably, the method also includes, prior to depositing the firstorganic layer, the steps of:

-   -   depositing a third organic layer comprising an organic material        of the third organic layer over the first electrode via solution        processing; and    -   depositing a fourth organic layer comprising an organic material        of the fourth organic layer over the third organic layer via        solution processing.        Preferably the third organic layer does not dissolve when the        fourth organic layer is deposited, and the fourth organic layer        does not dissolve when the first organic layer is deposited.

Preferably, the organic light emitting device emits light having a CIEcoordinate of x coordinate in the range of 0.15-0.65, and y coordinatein the range of 0.1-0.7. More preferably, the organic light emittingdevice emits light having a CIE coordinate of x coordinate in the rangeof 0.25-0.5, and y coordinate in the range of 0.2-0.5.

The layers may include materials other than those specified. Forexample, the first organic layer may further comprises a third organicemitting material of the first organic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows an organic light emitting device including a solutiondeposited emissive layer that includes co-doped emissive materials.

FIG. 4 shows an organic light emitting device including a solutiondeposited emissive layer that includes co-doped emissive materials, withmore detail than FIG. 3.

FIG. 5 shows an organic light emitting device including a vapordeposited emissive layer that includes co-doped emissive materials.

FIG. 6 shows a 1931 CIE diagram illustrating a CIE coordinate for awhite device having a solution deposited co-doped emissive layer.

FIG. 7 shows an emissive spectrum for the white device that generatedthe CIE coordinate of FIG. 6.

FIG. 8 shows a 1931 CIE diagram illustrating the variance in the CIEcoordinates of devices fabricated using a vapor deposition technique.

FIG. 9 shows a magnified portion of the 1931 CIE diagram of FIG. 8.

FIG. 10 shows spectra for the devices fabricated using a vapordeposition technique.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

An method of fabricating an organic light emitting device is provided. Afirst electrode is provided, over which the rest of the device will befabricated. A first organic layer is deposited over the first electrodevia solution processing. The first organic layer includes:

-   -   i. an organic host material of the first organic layer;    -   ii. a first organic emitting material of the first organic        layer;    -   iii. a second organic emitting material of the first organic        layer.        A second organic layer is deposited over and in direct contact        with the first organic layer. The second organic layer includes        an organic emitting material of the second organic layer. A        second electrode is then deposited over the second organic        layer. The device may include other layers.

FIG. 3 shows an example of device 300 fabricated using the describedmethod. The device is fabricated on a substrate 310. The device includesa first electrode 320, emitting layers 330 disposed over the firstelectrode 320, and a second electrode 340 disposed over the emittinglayers 330. Emitting layers 330 include first organic layer 332 andsecond organic layer 334. First electrode 320 is preferably an anode andsecond electrode 340 is preferably a cathode, but other configurationsmay be used.

First electrode 320 may be provided by any suitable method, includingthe purchase of commercially available substrates pre-coated with indiumtin oxide (ITO) or other electrode material. First organic layer 332 isdeposited via solution deposition over first electrode 320. The solutionused to deposit first organic layer 332 includes a solvent, the organichost material of the first organic layer; the first organic emittingmaterial of the first organic layer; and the second organic emittingmaterial of the first organic layer. Other materials may be included.Second organic layer 334 is deposited over and in direct contact withfirst organic layer 332. Second organic layer 334 includes an organicemitting material of the second organic layer. Second electrode 340 issubsequently deposited over second organic layer 334 by any suitabletechnique.

Device 300 as illustrated also includes optional layers. A third organiclayer 350 and a fourth organic layer 360 are disposed between emittinglayers 330 and first electrode 320. Where first electrode 320 is ananode, third organic layer 350 may be a hole injection layer and fourthorganic layer may be a hole transport layer. A fifth organic layer 370is disposed between emitting layers 330 and second electrode 340. Wheresecond electrode 340 is a cathode, fourth organic layer 370 may includea hole blocking layer, and an electron transport layer. Third, fourthand fifth organic layers 350, 360 and 370 may include sublayers, and mayinclude other layers useful in various OLED architectures, many of whichare described with respect to FIGS. 1 and 2.

Preferably, the first organic emitting material of first organic layer332 has a peak emissive wavelength in the visible spectrum of 590-700nm, the second organic emitting material of first organic layer 332 hasa peak emissive wavelength in the visible spectrum at 500-590 nm and theorganic emitting material of second organic layer 334 has a peakemissive wavelength in the visible spectrum of 400-500 nm. These peakwavelengths correspond roughly to red, green, and blue emitters, and areuseful for obtaining a device that emits white light that would beuseful, for example, for general illumination purposes.

Preferably, the first organic emitting material of first organic layer332 is present in first organic layer 332 in a concentration of 0.01-5wt %, and the second organic emitting material of first organic layer332 is present in the first organic layer in a concentration that is 1.1to 500 times the concentration of the concentration of the first organicemitting material. In addition, the second organic emitting material offirst organic layer 332 is present in an amount not more than 40 wt %.Percentages are given as weight percentages of the organic layer afterfabrication, and may generally be determined by using the relativeweight percentages in solution of the various materials to be deposited,because the solvent evaporates. More preferably, the first organicemitting material of first organic layer 332 is present in the in firstorganic layer 332 in a concentration of 0.2-4 wt %, and the secondorganic emitting material of first organic layer 332 is present in firstorganic layer 332 in a concentration that is 2 to 200 times theconcentration of the concentration of the first organic emittingmaterial. In addition, the second organic emitting material of firstorganic layer 332 is preferably present in an amount not more than 40 wt%.

Preferably, the first organic emitting material of first organic layer332, the second organic emitting material of first organic layer 332,and the organic emitting material of second organic layer 334 are allsmall molecule materials. Many small molecule materials are suitable forsolution deposition, or may be readily modified to render them suitablefor solution deposition using known techniques involving the addition ofbulky substituents.

Preferably, second organic layer 334 comprises an organic host and theorganic emitting material of second organic layer 334. Preferably,second organic 334 layer is deposited by vapor deposition, where theorganic host of second organic layer 334 and the organic emittingmaterial of second organic layer 334 are co-deposited. Vapor depositionincludes vapor thermal evaporation (VTE), organic vapor phase deposition(OVPD), and organic vapor jet printing (OVJP). Vapor deposition ispreferred because treatments to render underlying layers (such as firstorganic layer 332) insolvent often involve steps that would bedetrimental to emitting materials. However, where techniques exist forsolution depositing one emissive layer over another, those techniquesmay be used to deposit second organic layer 334 over first organic layer332.

Third and fourth organic layers 350 and 360, when present, arepreferably deposited via solution deposition techniques. Because theseorganic layers do not include emitting materials, material andprocessing choices are readily available that render these layersinsoluble in a solvent used to deposit subsequent layers. One suchprocess choice is baking to cross-link the material, rendering itinsoluble.

Preferably, the organic light emitting device emits light having a CIEcoordinate of x coordinate in the range of 0.15-0.65, and y coordinatein the range of 0.1-0.7. More preferably, the organic light emittingdevice emits light having a CIE coordinate of x coordinate in the rangeof 0.25-0.5, and y coordinate in the range of 0.2-0.5. These CIEcoordinates are readily obtainable using the preferred peak wavelengthchoices for the emitting materials of the device.

One issue that the inventors have identified and solved relates to thefirst organic layer. The preferred percentages are useful forfabricating a device that emits white light. However, using thepreferred wavelengths and amounts for the first and second emittingmaterials of first organic layer 332 means that first organic layer 332includes a small amount of red dopant, and a larger amount of greendopant. To achieve white emission from the overall device, the amount ofred dopant will generally be small, both in absolute terms and relativeto the amount of green dopant. This is because when a red dopant isco-doped with a green dopant, excitons may preferentially move to thered dopant or transfer from the green dopant to the red dopant due tothe lower energy of the red dopant. Due to this preferential emissionfrom the red dopant, a significantly smaller amount of red and largeramount of green is needed than if the materials were in separate layers.In addition, the amount of emission from red dopant relative to greendopant is highly sensitive to small variations in the concentrations ofthe dopants, again due to the preferential emission from the red dopant.

Controlling the amount of dopant deposited via vapor depositiontechniques such as VTE generally involves adjusting temperatures,aperture sizes and relative flow rates of materials. The variance in theamount of dopant deposited from run to run is typically about 5%. So ifit were desired to deposit a layer having 1 wt % of red dopant, theactual amount of red dopant would be about 0.95 wt % to 1.05 wt %. Wherethe device includes a layer having co-doped red and green dopants (andthe green dopant will also be expected to have a 5% variance), thevariance is large enough to significantly alter the CIE coordinates of adevice.

However, controlling the amount of dopant for solution processtechniques generally involves weighing the various materials and addingthem to a solvent in carefully controlled amounts. In the inventorslaboratory, a weight as low as 0.001 g of red dopant can be measured foruse in solution using a micro balance with a precision of 0.00001 g(plus or minus). In this case, variance is 1%. This reduction invariance is expected to significantly improve the reproducibility of theCIE coordinates of the finished device.

Particularly preferred concentrations for a layer including only red andgreen dopants are about 1 wt % for the red dopant and about 12 wt % forthe green dopant. Other combinations of dopants, and otherconcentrations may be used. A solution processed emitting layer mayinclude three or more emitting materials. An example of this useful fora white-emitting device is a layer that includes 72 wt % host, 20 wt %green emitter, 5 wt % yellow and 3 wt % red. Another example is 68.9 wt% host, 30 wt % green, 1% red1, and 0.1% red2 where red1 and red2 aredifferent red emitting materials.

Other types of dopants may be used, and dopants in addition to thosespecifically described may be used. For example, the first organic layermay further comprises a third organic emitting material of the firstorganic layer. A third organic dopant may be useful, for example, to addan additional emission color to fine tune the overall emission of thedevice, to adjust conductivity, or other uses.

Emissive “dopants” may include phosphorescent emitting organic materialsor fluorescent organic emitting materials.

A preferred device structure is illustrated in FIG. 4. Device 400 is apreferred specific structure of device 300. Device 400 is fabricated ona substrate 410, and includes, in order, anode 420, solution processedorganic hole injection layer 452, solution processed organic holetransport layer 454, solution processed organic emissive layer 432, VTEdeposited organic emissive layer 434, VTE deposited organic blockinglayer 462, VTE deposited organic electron transport layer 464 andcathode 440. Solution processed organic emissive layer 432 includes ahost and red and green emitting dopants, and VTE deposited organicemissive layer 434 includes a host and a blue emitting dopant.

FIG. 5 shows a comparative example that does not include a solutiondeposited layer having multiple emissive dopants. Device 500 isfabricated on a substrate 510, and includes, in order, anode 520, VTEdeposited organic hole injection layer 552, VTE deposited organic holetransport layer 554, VTE deposited organic emissive layer 532, VTEdeposited organic emissive layer 534, VTE deposited organic blockinglayer 562, VTE deposited organic electron transport layer 464 andcathode 440. VTE deposited organic emissive layer 532 includes a hostand red and green emitting dopants, and VTE deposited organic emissivelayer 534 includes a host and a blue emitting dopant.

FIG. 6 shows a CIE diagram. The star is located at a target CIEcoordinate that is desirable for white emission. The curve on which thestar is located is the well-known black-body radiation curve, whichdescribes the color of thermal radiation from an object that absorbs allelectromagnetic radiation that falls on it (a “black body”). FIG. 7shows a target spectrum calculated using the emission spectra of thered, green and blue emitting materials of Example 1.

Materials

The following materials were used in the Examples:

LG101 and LG201, available for purchase from LG Chemical Corporation ofSeoul, Korea. NS60, available for purchase from Nippon Steel ChemicalCompany of Tokyo, Japan.

EXAMPLES Example 1 All VTE White Device (Comparative Example)

As a comparative example, white OLEDs were fabricated using standardvacuum thermal evaporation (VTE) techniques to fabricate the entiredevice. These devices had the structure shown in FIG. 5. The materialsand thicknesses of the layers were as follows:

ITO (80 nm)/LG101 (10 nm)/NPD (45 nm)/NS-60:Green Dopent:Red Dopant-1(69:30:1; 20 nm)/Host-2:Blue Dopant-1: (80:20; 7.5 nm)/Host-2 (5nm)/LG201 (45 nm)/LiF/AlSeven VTE white devices were fabricated in different batches. Theemission of these devices was measured, and the CIE coordinates of thedevices are plotted in FIGS. 8 and 9. All seven devices were carefullymade to have the same in structure, composition, and thickness. However,the colors are quite different by different batches. The average CIEcoordinate of 7 batches is (0.424±0.007, 0.413±0.014).

The color difference between different devices can be described byMacAdam Ellipses, which are a well-known measure of human ability todifferentiate color. A MacAdam Ellipse is a region on a CIE diagraminside of which a particular number of humans can not differentiatebetween colors. At a distance of one “step,” from a target CIEcoordinate, 68% of people can perceive a color difference. 68% is thepercentage that falls within one standard deviation on a bell curve. Ata distance of two steps, 95% of people can perceive a color difference,where 95% is the percentage that falls within two standard deviations ona bell curve, and so on. The lighting industry generally desires thatthe color of a light used for illumination be reproducible within a 3-or 4-step MacAdam ellipse. If color reproducibility is too low, a viewerlooking at two sources of illumination would perceive significantdifferences. For example, the different panels of a ceiling light mightappear to have different colors, or there might be a significantlyperceivable variation within a panel, which is undesirable.

FIG. 8 shows the CIE coordinates of the seven devices having thestructure shown in FIG. 5. FIG. 9 shows the same data as FIG. 8, but therelevant region of the diagram is magnified. FIG. 10 shows the measuredspectra for the seven devices. It can be seen that there is asignificant spread in the CIE coordinates of the different devices, andthat they are all well outside of a 3-step MacAdam ellipse centeredaround the average of the CIE coordinates (0.424, 0.413) of the sevendevices. The 7-step MacAdam ellipse can barely enclose the 7 devicecolors, which is out of industrial standard tolerance specification.This means that color reproducibility is not reliable for the VTEdevices notwithstanding the care taken to achieve color reproducibility.The inventors attribute this variation in color to the sensitivity ofthe co-doped green and red emitting layer to the percentage of reddopant, and the relatively high variation in this percentage that occurswith a VTE deposition process.

Example 2 Hybrid White Device

A device was fabricated having the structure shown in FIG. 4. The holeinjecting material HIL-1 (as the host material) along with Conductingdopant-1 were dissolved in a cyclohexanone solution. The amount ofConducting dopant-1 in the solution was 10 wt % relative to the hostmaterial HIL-1. The total concentration of the HIL-1 and Conductingdopant-1 was 0.5 wt % in cyclohexanone. To form the hole injection layer(HIL), the solution was spin-coated at 4000 rpm for 60 seconds onto apatterned indium tin oxide (ITO) electrode. The resulting film was bakedfor 30 minutes at 250° C. The film became insoluble after baking.

On top of the HIL, a hole transporting layer (HTL) and then emittinglayer (EML) were also formed by spin-coating. The HTL was made byspin-coating a 1 wt % solution of the hole transporting material HTL-1in toluene at 4000 rpm for 60 seconds. The HTL film was baked at 200° C.for 30 minutes. After baking, the HTL became an insoluble film.

The red and green EML was composed of a host material (Host-1) and a redand a green phosphorescent dopant (Red dopant-1 and Green dopant-1) asthe emitting material. To form the EML, a toluene solution containingHost-1, Green dopant-1, and Red dopant (of total 0.75 wt %) with aHost-1:Green dopant-11:Red dopant-1 weight ratio of 87:12:1, wasspin-coated onto the insoluble HTL at 1000 rpm for 60 seconds, and thenbaked at 100° C. for 60 minutes.

The blue EML was deposited using thermal evaporation. The 10 nm of bluehost (Host-2) and Blue dopant-1 was co-evaporated with ratio of 90:10.On top of blue EML, 5 nm neat Host-2 was evaporated to build blockinglayer (BL). The electron transport layer (containing Alq3), the electroninjection layer (containing LiF), and the aluminum electrode weresequentially vacuum deposited.

When finished, the device of Example 2 had the structure:

ITO (120 nm)/HIL-1:Conducting Dopant-1 (90:10; 5 nm)/HTL-1 (10nm)/Host-1:Green Dopant-1:Red Dopant-1 (87:12:1; 25 nm)/Host-2:BlueDopant-1: (90:10; 10 nm)/Host-2 (5 nm)/Alq (40 nm)/LiF/Al

The CIE coordinate and spectrum of the hybrid white device of Example 2are shown in FIGS. 6 and 7, respectively. The device performance isdescribed in TABLE 1. At 1000 cd/m2, the power efficiency was 11 lm/Wwith color rendering index (CRI) 78, and correlated color temperature(CCT) corresponding to the white color was 2800K degree.

TABLE 1 Hybrid white device performances of Example 2 Power Efficiency(lm/W) @ 1,000 cd/m2 11 Correlated Color Temperature (CCT) (K) @ 1,000cd/m2 2800 Color Rendering Index (CRI) @ 1,000 cd/m2 78 ColorCoordinate, CIE(x, y) @ 1,000 cd/m2 (0.453, 0.411) Lifetime LT80 (hours)@ 4,000 cd/m2 100 (A brightness decay to 80% of initial level 4,000cd/m2)

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1-10. (canceled)
 11. A method comprising: a. providing a firstelectrode; b. depositing a first organic layer over the first electrodevia solution processing, the first organic layer further comprising: i.an organic host material of the first organic layer; ii. a first organicemitting material of the first organic layer; iii. a second organicemitting material of the first organic layer; iv. a third organicemitting material of the first organic layer; wherein the first, thesecond, and the third organic emitting materials are co-doped in theorganic host material; c. depositing a second electrode over the firstorganic layer.
 12. The method of claim 11, wherein: a. the first organicemitting material of the first organic layer has a peak emissivewavelength in the visible spectrum of 590-700 nm; b. the second organicemitting material of the first organic layer has a peak emissivewavelength in the visible spectrum at 570-590 nm; and c. the thirdorganic emitting material of the first organic layer has a peak emissivewavelength in the visible spectrum of 500-570 nm.
 13. The method ofclaim 11, wherein the organic light emitting device emits light having aCIE coordinate of x coordinate in the range of 0.15-0.65, and ycoordinate in the range of 0.1-0.7.
 14. The method of claim 13, whereinthe organic light emitting device emits light having a CIE coordinate ofx coordinate in the range of 0.25-0.5, and y coordinate in the range of0.2-0.5.
 15. The method of claim 11, further comprising, prior todepositing a second electrode over the first organic layer: depositing asecond organic layer over the first organic layer, the second organiclayer further comprising: i. an organic host material of the secondorganic layer; and ii. an organic emitting material of the secondorganic layer.
 16. The method of claim 15, wherein: the second organiclayer is deposited by vapor deposition, wherein the organic host of thesecond organic layer and the organic emitting material of the secondorganic layer are co-deposited.
 17. The method of claim 1, wherein thefirst organic emitting material of the first organic layer, the secondorganic emitting material of the first organic layer, and the organicemitting material of the second organic layer are all small moleculematerials.
 18. The product of claim 11, the fabrication process furthercomprising, prior to depositing the first organic layer: a. depositing athird organic layer comprising an organic material of the third organiclayer over the first electrode via solution processing; b. depositing afourth organic layer comprising an organic material of the fourthorganic layer over the third organic layer via solution processingwherein the third organic layer does not dissolve when the fourthorganic layer is deposited, and the fourth organic layer does notdissolve when the first organic layer is deposited.